The invention relates to a method and apparatus for visualizing the directional sound activity of a multichannel audio signal.
Audio is an important medium for conveying any kind of information, especially sound direction information. Indeed, the human auditory system is more effective than the visual system for surveillance tasks. Thanks to the development of multichannel audio format, spatialization has become a common feature in all domains of audio: movies, video games, virtual reality, music, etc. For instance, when playing a First Person Shooting (FPS) game using a multichannel sound system (5.1 or 7.1 surround sound), it is possible to localize enemies thanks to their sounds.
Typically, such sounds are mixed onto multiple audio channels, wherein each channel is fed to a dedicated loudspeaker. Distribution of a sound to the different channels is adapted to the configuration of the dedicated playback system (positions of the loudspeakers), so as to reproduce the intended directionality of said sound.
Multichannel audio streams thus require to be played back over suitable loudspeaker layouts. For instance, each of the channels of a five channel formatted audio signal is associated with its corresponding loudspeaker within a five loudspeaker array. FIG. 1 shows an example of a five channel loudspeaker layout recommended by the International Telecommunication Union (ITU), with a left loudspeaker L, right loudspeaker R, center loudspeaker C, surround left loudspeaker LS and surround right loudspeaker RS, arranged around a recommended listener's position P. With this recommended listener's position P as a center, the relative angular distances between the central directions of the loudspeakers are indicated.
If multichannel audio is played back over an appropriate sound system, i.e. with the required number of loudspeakers and correct angular distances between them, a normal hearing listener is able to detect the location of the sound sources that compose the multichannel audio mix. However, should the sound system exhibit inappropriate features, such as too few loudspeakers, or an inaccurate angular distance thereof, the directional information of the audio content may not be delivered properly to the listener. This is especially the case when sound is played back over headphones.
As a consequence, there is in this case a loss of information since the multichannel audio signal conveys sound direction information through the respective sound levels of the channels, but such information cannot be delivered to the user. Accordingly, there is a need for conveying to the user the sound direction information encoded in the multichannel audio signal.
Some methods have been provided for conveying directional information related to sound through the visual modality. However, these methods were often a mere juxtaposition of volume meters, each dedicated to a particular loudspeaker, and thus unable to render precisely the simultaneous predominant direction of the sounds that compose the multichannel audio mix except in the case of one unique virtual sound source whose direction coincides with a loudspeaker direction. Other methods intended to more precisely display sound locations are so complicated that they reveal themselves inadequate since sound directions cannot be readily derived by a user.
For example, U.S. patent application US 2009/0182564 describes a method wherein sound power level of each channel is displayed, or alternatively wherein position and power level of elementary sound components are displayed.